The present invention relates to a process for preparing cyclic acetals of aliphatic, saturated aldehydes.
Cyclic trimers, such as the 2,4,6-trialkyl-(1,3,5)-trioxanes, and tetramers of aliphatic, saturated aldehydes are formed by the action of acid catalysts, such as sulphuric acid, hydrochloric acid or phosphoric acid, or ion exchangers. In general, the aldehydes are passed into an acidified solution while stirring and cooling. After the conclusion of the reaction, the mixture is neutralized with sodium bicarbonate or sodium carbonate. Care must be taken to adjust the equivalent point accurately in order to avoid aldolization reactions in alkaline solutions. The reaction mixture is then distilled in order to remove the salts formed and the water.
Continuous cyclization is carried out by passing aldehydes over acid cation exchangers, but the latter have a limited life. Their properties undergo variation after a short time because of condensation reactions with the reactive aldehydes and because the ion exchangers begin to swell due to the good solubility properties of the aldehydes.